rule out diabetes as it could be one of the reason.

make sure it's not infected

Consult a dermatologist for examination, particularly because walking has become painful. Wear comfortable, cushioned footwear and avoid walking barefoot. Use a soft donut-shaped protective pad to reduce pressure on the affected area. If a corn is confirmed, treatment may involve careful removal of thickened skin or appropriate keratolytic preparations. If a plantar wart is diagnosed, treatment options include salicylic acid preparations or cryotherapy, depending on the lesion. Avoid cutting, digging, or attempting to remove the black spot yourself.

Keep your feet clean and dry, and avoid tight footwear that increases pressure. Do not use corn-removal acids without medical advice, particularly if you have diabetes, poor circulation, or reduced sensation in your feet. Seek medical attention if you develop increasing redness, swelling, discharge, fever, or severe worsening of pain. A black spot that enlarges, changes colour, bleeds, or fails to heal also needs prompt dermatological assessment. My recommendation: Since the lesion is painful and affecting your ability to walk, have it examined before starting corn-removal treatment. Most corns and plantar warts can be managed effectively once correctly diagnosed. Wishing you a speedy recovery!